1. Field of the Invention
This invention relates to an elevator having a car which ascends and descends within a shaft, in particular, a structure for firmly fixing sheaves, around which a hoisting cable passes, on a car frame which supports the car.
2. Description of the Related Art
Machine-roomless elevators, which needs no machine room projecting above the shaft, require less space, and have many advantages, such as the building is less influenced by height limitation. For example, in a machine-roomless elevator disclosed in Japanese Patent Publication (KOKAI) No. 2004-189346, a car frame which supports the car is equipped with a pair of sheaves. The sheaves are supported by an upper beam of the car frame through a sheave support beam. A cable from which the car is suspended in the shaft passes around the sheaves.
The sheave support beam is fixed on the lower surface of the upper beam, in the state of being crossed with respect to the upper beam. A bracket is attached to one longitudinal end and the other end of the sheave support beam. The brackets project upward from the sheave support beam. Each sheave is rotatably supported by the brackets, and located on sides of the upper beam.
According to the above structure, the rotational axis line of the sheaves is located above the lower surface of the upper beam, and thus the upper beam can be located as close as possible to the ceiling of the car. Thereby, when the car is hoisted to the uppermost portion of the shaft, the overhead between the uppermost portion of the shaft and the ceiling of the car can be reduced.
According to the sheave support structure disclosed in the above patent publication, the brackets which support the sheaves are only fixed at lower ends on the sheave support beam. In other words, the upper ends of the brackets are free ends which are not bound at all. Therefore, when the sheaves are rotated with raising or lowering of the car, there is the limit for the brackets to firmly support the sheaves. Thus, the position of the sheaves with respect to the sheave support beam easily becomes unstable, and it is inevitable that the sheaves vibrate in the thrust direction. Vibration of the sheaves occurring in raising or lowering of the car causes problems, such as promotion of vibration conducted from the cable to the car through the sheaves and occurrence of noise.